+1 -----Original Message----- From: Af [mailto:[email protected]] On Behalf Of Jay Weekley Sent: Wednesday, February 17, 2016 10:26 AM To: [email protected] Subject: Re: [AFMUG] 450i 900 using existing yagi
Dr. McCown. If separation is important then how do they get away with making both antennas essentially the same unit? I'm sure there is a simple explanation. Chuck McCown wrote: > Somewhere, in one of my 50 or so antenna books, there is a graph > showing mutual coupling of yagi antennas mounted on the same mast with > respect to separation. Right now, I am 50 miles away from those books. > As I recall, if they are cross polarized, there is very little > coupling at close distances. > I think there is theoretically zero coupling of the far field. But > you get strong reactive nearfield effects at 900 MHz around the 7 inch > range or less. That just means that the two antennas will start > throwing off the impedance and resonant frequency of the other one > the closer they get. > However there is the Radiating Nearfield Distance too. If you are > inside that limit the two will mess with each others patterns pretty > bad. That is on the order of 22 inches. However due to being cross > polarized the effects should not be strong. > So, yeah... 2 feet is good if cross pol. I don’t think I would not go > under 1 foot. > If you have some time, experiment a bit. > *From:* Brandon Yuchasz <mailto:[email protected]> > *Sent:* Tuesday, February 16, 2016 9:09 PM > *To:* [email protected] <mailto:[email protected]> > *Subject:* [AFMUG] 450i 900 using existing yagi > > Since we are now deploying some 450 900 gear we are pulling down lots > of old FSK with M2 Yagi antennas. In general I really like the Cambium > yagi they are well thought out and the SM being mounted on it is > really clean. Swaps are a breeze. That said I am still thinking about > using the M2 in specific situations like tripods. I did some > retrofitting today to convert two to slant and we went and tested and > got good results. There were separated from each other vertically > about 8 inches at the mounting brackets and I didn’t see any issues . > We got 8x8x line of site. > > So my question to the group is, in general is there a rule of thumb to > use for vertical separation on dual polarity antennas being mounted > like this? Could they be stacked tight near each other? > > Best regards, > > Brandon Yuchasz > > GogebicRange.net > > www.gogebicrange.net <http://www.gogebicrange.net/> >
